In a Session Initiation Protocol (SIP) based communications network SIP transactions, such as SIP Invite transactions, are performed. According to known methods, these transactions generally include SIP messages being sent from a first node to a third node via a second node. For example during a SIP call, SIP messages may be transmitted from a User Agent (UA) via a Proxy Call Session Control Function (P-CSCF) entity to a Serving Call Session Control Function (S-CSCF) entity, from a P-CSCF via an S-CSCF entity to an Interrogating Call Session Control Function (I-CSCF) entity, or from a first S-CSCF entity via an I-CSCF entity to a second S-CSCF entity.